1. Field of the Invention
The present invention relates to an image forming apparatus and method for performing image formation and lamination of a protection layer on an image to protect the image formed on a print recording medium.
2. Description of the Related Art
Image forming apparatuses include those of a sublimation type in which color materials, such as dyes, of a thermal transfer sheet are transferred onto a print recording medium to thereby form an image on the medium. In an apparatus of this type, a transparent protection layer is additionally formed on an image to protect the image formed on the print recording medium. The protection layer has functions of, for example, shielding an image from gases potentially causing image deterioration, preventing the image from discoloration associated with absorption of UV light, preventing image-forming color materials, such as dyes, from being transferred to an article including various plasticizers, such as erasing rubber, preventing the image from frictional wear, and protecting the image from sebum.
Such a protection layer is provided by being laminated on, for example, a film-shaped base material, and is thermally transferred thereonto by a thermal head. In addition to the image protection capability, the protection layer thus thermally transferred onto the image is able to prevent curling of the print recording medium. Further, depending on the case, in the event of thermal transfer being performed by using the thermal head, thermal energy incoming from the thermal head is arbitrarily varied. In this case, a small concave-convex pattern is formed with the protection layer on the surface of the medium, and the surface is arbitrarily treated to form a silky pattern, mat pattern, or lustrous pattern.
However, problems such as described below can occur when performing the surface treatment of the image during image formation and protection film lamination. In the event of image formation, concave portions occur on a printed surface in a high density print region such as dark color region. Thereby, cases can take place in which concave-convex portions corresponding to the gradation level of the image mixedly occur in the print region to the extent of degrading quality of the printed surface. This problem can possibly provide adverse effects on print quality after the protection layer is formed on the image. More specifically, in a portion where concave portions attributed to the high density print region have occurred, the concave portions affect the surface pattern of the protection layer, which is formed in the subsequent stage, to be nonuniform. As such, in the event of the surface treatment of the protection layer, also the profile of a small concave-convex pattern formed by the surface treatment becomes nonuniform, thereby degrading quality of the printed surface.
The image forming apparatuses of the above-described type include those that implement high speed printing by increasing a travel speed of a print recording medium to a highest possible level. In this case, the travel speed of the print recording medium is increased to the highest possible level not only in the event of image formation, but also in the event of protection layer formation. As such, depending on the case, compared to the past or existing techniques in which a transport speed of the print recording medium is not increased, the time period for application of pressure and thermal energy to the protection layer is shorter, thereby causing the profile of the small concave-convex pattern formed after image protection layer transfer to be unclear.